Topical anesthetics such as lidocaine, benzocaine and the like are widely used to treat pain and itching associated with insect bites, sunburn, contact dermatitis, and in connection with anal-rectal conditions such as hemorrhoids, fissures and infections. Most preferably, the topical anesthetic material is disposed in a carrier which is a cream, lotion or gel, and in many instances, liposomal structures are particularly favored carriers. As is known in the art, liposomal structures comprise vesicles having walls formed from a phospholipid or similar material.
In general, the efficacy of the anesthetic containing compositions is directly dependent upon the concentration of anesthetic therein. Heretofore, lidocaine containing compositions, particularly those compositions formulated for topical application and/or encapsulated in liposomes, have been restricted to concentrations of approximately 2-5% lidocaine. Such compositions are shown in U.S. Pat. Nos. 4,937,078 and 6,045,824. Prior to the present invention, the art has not been able to prepare stable lidocaine containing preparations which are suitable for topical application to the skin, and in which the concentration of lidocaine is greater than 10%.
As will be explained in detail herein below, the present invention comprises lidocaine compositions having a weight percentage of lidocaine therein of at least 10%. The compositions of the present invention are generally prepared as liposome based compositions in which the lidocaine is disposed in a non-aqueous phase encapsulated within liposomes and wherein the liposomes are disposed in a continuous, aqueous phase. The overall concentration, by weight, of the lidocaine in the compositions is over 10%, and preferably 12% or more by weight. The compositions of the present invention are easy to prepare and stable on storage. Also within the scope of the present invention are methods for the preparation of the compositions.